1. 1 Lecture 7b DWDM 1. Introduction 2. Principles of Wavelength Division Multiplexing 3. WDM System Components 4. Wavelength-Independent Coupler 5. Construction of Wavelength Independent Couplers 6. Wavelength-Dependent Coupler (Multiplexer/Demultiplexer) 7. WDM Communication System 8. Dense Wavelength Division Multiplexing (DWDM) 9. Add-drop Multiplexer 10. Conclusion 11. Appendix

2. 2 Time Division Multiplexing (TDM) Wavelength Division Multiplexing (WDM) TDM divides a high-bandwidth transmitted signal into time slots. Each time slot carries a different low-bandwidth signal. In WDM, several high-bandwidth signals travel on the same fiber, in the same time, each using a different light wavelength. DWDM uses the same principles as a WDM, but with high density of light wavelength alocation. A common application of multiplexing is in long- distance data and voice communications.

3. 3 Access techniques for mobile communications P - Power T - Time F - Frequency P T P T F P T F FDMA (TACS) TDMA (GSM, DECT) CDMA (UMTS) F ATDMA (UMTS)

4. 4 Principles of Wavelength Division Multiplexing (WDM)

5. 5 WDM System Components A coupler combiner, and a splitter, Couplers are bi-directional devices; Wavelength Independent Wavelength Dependent

6. 6 Wavelength-Independent Coupler

7. 7 Input power = 1 mW Splitting ratio of each coupler = 9:1 Excess loss of each coupler = 0.3 dB Insertion loss of each connector = 0.2 dB The input power is 1 mW, so we can express the power as zero decibel milliwatts (0 dBm). The incoming power level to first splitter is reduced by 0.2 dB by the first connector, and 0.3 dB by the excess loss. At the first splitter, we have total power of - 0.5 dBm, or:

8. 8 Construction of a Wavelength Independent Coupler

9. 9 Wavelength-Dependent Couplers (Multiplexer / Demultiplexer)

10. 10 (8.5)

11. 11

12. 12 WDM Communication System (8.6)

13. 13

14. 14 Several modulated laser sources, one for each optical channel. A Distributed Feedback (DFB) laser is the best source for a DWDM system, narrow bandwidth, (less than 0.4 nm). Modulation Erbium Doped Fiber Amplifier (EDFA), An optical demultiplexer to separate each signal at its destination. Suitable detectors for each signal to extract the information in that. A DWDM system can be designed with 41 channels in the range of 1528 nm to 1561 nm. DWDM can increase the capacity of a single fiber to as much as several hundred gigabits per second. This is the same capacity as several thousand 100Base-T Ethernet cables.

15. 15 Stimulated Emission 1520-1620 nm -1 mks Short- wavelength Source (980 nm) Longer- wavelength Source (1480 nm) Excited erbium atoms at high energy level Atoms at metastable energy (-10 ms) Erbium atoms at low energy level